Voice communication is evolving from circuit-switched technology, such as provided by the Public Switched Telephone Network (PSTN) or Public Land Mobile Network (PLMN), to packet-switched technology, such as provided by Voice over IP (VoIP) techniques across Internet Protocol (IP) networks. At the same time, wireless networks are evolving from circuit-switched voice networks (e.g., GSM (Global System for Mobile communications), IS-136 (Time Division Multiple Access (TDMA)), and IS-95 (Code Division Multiple Access (CDMA))) to packet-switched networks (e.g., WLAN (Wireless Local Area Network), UMTS (Universal Mobile Telecommunication System), and CDMA2000) capable of supporting multimedia applications to mobile end-users over IP. General Packet Radio Service (GPRS), which is an evolution of GSM, can support packet data (e.g., web browsing, email, etc.) in a cellular environment. Further evolution of GPRS, often referred to as UMTS, is expected to support real-time multimedia over IP (e.g., VoIP, video over IP, streaming media, etc.) in a cellular environment. In addition, the Third Generation Partnership Project (3GPP) has specified the IP Multimedia Subsystem (IMS) to accomplish the control and service functions of wireless IP multimedia. In this regard, the 3GPP has adopted Session Initiation Protocol (SIP) as the signaling protocol in IMS.
With the availability of both packet-switched networks and circuit-switched networks, voice calls must sometimes be handed over from one type of network, such as a packet-switched network or a circuit-switched network, to the other type of network. For example, the 3GPP includes a single radio voice call continuity (SR-VCC) feature for allowing a voice call to be handed over from a packet-switched connection to a circuit-switched connection, for example, thereby permitting a VoIP call over a data bearer to be handed over to a traditional voice call over a circuit-switched bearer. As such, VoIP services can be more widely utilized by providing interworking between circuit-switched networks and packet-switched networks.
In order to provide a secure connection for communication via either a circuit-switched network or a packet-switched network, security keys are defined by both the user equipment, such as a mobile station, and a network entity, such as a serving GPRS support node (SGSN) in a packet-switched network and a mobile switching center (MSC) server in a circuit-switched network. However, upon handover between a packet-switched network and a circuit-switched network, there may be an initial period in which communications are conducted with no security protection, while security keys, such as a cipher key and an integrity key and the like, are provisioned in the new network, such as in a circuit-switched network in response to handover from a packet-switched network to the circuit-switched network. In this regard, while the subscriber identity module (SIM) of the user equipment, such as a mobile station, and a visitor location register (VLR) associated with an MSC server may sometimes store security keys for the circuit-switched network, such security keys for the circuit-switched network are not always stored or available. In instances in which the circuit-switched security keys are not stored, the circuit-switched security keys must be newly generated, which may result in the initial period following handover in which communications would be conducted via the circuit-switched network without security. As will be apparent, any period during which communications are unsecured is undesirable.
As such, it would be advantageous to provide an improved mechanism for providing security in a response to a handover between a packet-switched network and a circuit-switched network. In this regard, it would be desirable to provide an improved mechanism for insuring that all communications, including communications during the initial period, following a handover between a packet-switched network and a circuit-switched network are secured.